Regulating apparatus for generators



Oct. 25, 1960 H. MlTTAG ETAL REGULATING APPARATUS FOR GENERATORS FiledJan. 20, 1958 Fig. 7

2 Sheets-Sheet 1 INVENTORS Oct. 25, 1960, H. MITTAG ETAL 2,958,033

REGULATING APPARATUS FOR GENERATORS Filed Jan. 20, 1958 2 Sheets-Sheet 2INVENTOR$ United States Patent REGULATING APPARATUS FOR GENERATORSHermann Mittag, Stuttgart-Botnang, and Kurt Paule,Stuttgart-Oberturkheim, Germany, assignors to Robert Bosch, G.m.b.H.,Stuttgart, Germany Filed Jan. 20, 1958, Ser. No. 710,029

Claims priority, application Germany July 14, 1956 23 Claims. (Cl.322-25) The present invention relates to a regulating arrangement. Moreparticularly, the present invention relates to an apparatus forautomatically regulating the voltage output of an electrical generator.

This application is a continuation-in-part of our now abandonedapplication Serial No. 671,950, filed July 15, 1957, entitled RegulatingApparatus.

The present invention is primarily applicable to electrical generatorswhich are found on motor vehicles for supplying the electrical energyfor operating the lights and the other electrical apparatus used on suchmotor vehicles. It is well known that the conventional voltageregulators all use certain types of contacts which become pitted withuse. These pitted contacts tend to stick and provide major maintenancedifliculties in the voltage regulation system of the motor vehicles.

It is accordingly an object of the present invention to provide anapparatus which overcomes the disadvantages of the prior artarrangements.

A second object of the present invention is to provide a new andimproved apparatus for regulating the voltage output of shunt woundgenerators.

Another object of the present invention is to provide a voltageregulator for generators used on motor vehicles wherein the voltageregulator uses no movable contacts.

Still another object of the present invention is to provide a new andimproved voltage regulator for shunt wound generators, which voltageregulator uses transistors.

A further object of the present invention is to provide a new andimproved voltage regulator which regulates the voltage output of shuntwound generators and which controls the current output thereof.

Yet a further object of the present invention is to provide a voltageregulator for electrical generators wherein one transistor is controlledby a second transistor which in turn is varied by the voltage output ofthe electrical generator.

Still a further object of the present invention is to provide a voltageregulator of the type set forth in which the voltage output of thegenerator remains substantially constant up to a preselected value ofthe output current of the generator, while the voltage decreases rapidlywhenever the output current exceeds the preselected value.

With the above objects in view, the present invention mainly consists ofan apparatus for regulating the voltage output of an electricalgenerator having a shunt field exciting winding adapted to have excitingcurrent flow therethrough. This apparatus includes variable impedancemeans in the form-of a first transistor which is connected in circuitwith the shunt winding of the electrical generator for adjusting theexciting current flowing through the shunt winding in accordance withthe impedance thereof and thereby to adjust the voltage output of thegenerator. Control means are utilized in the apparatus, the controlmeans including a second transistor and having an input circuitconnected in circuit with the output of the generator and having anoutput circuit connectedin Patented Oct. 25, 1960 circuit with the firsttransistor to produce an output current. The output current varies theimpedance of the first transistor which in turn varies the voltageoutput of the generator. Accordingly, any change in the voltage outputof the electrical generator will change the output current of the secondtransistor to produce a corresponding change in the impedance of thefirst transistor and in the exciting current flowing through the shuntfield winding to thereby change the voltage output of the generator in apreselected manner.

In a preferred embodiment of the present invention, the generator has aself-exciting field winding so that the variable impedance means isconnected between the voltage output of the generator and the shuntfield winding to supply exciting current for the shunt field winding.

The variable impedance means can be a first transistor having electrodesconnected in circuit with the shunt field winding, which transistorregulates the current flowing through the shunt field winding inaccordance with the potential distribution between the variouselectrodes of the transistor. In such a case, the control means can be asecond transistor which is placed in self-oscillating condition when thevoltage output reaches a preselected level. The output current of thesecond transistor changes the potential distribution between theelectrodes of the first transistor so that the current through the fieldwinding is changed in a direction to maintain the generator voltageoutput at the preselected level.

In one embodiment of the present invention, an auxiliary battery isarranged in circuit with the second transistor utilized as the controlmeans.

In still another embodiment, such auxiliary battery is eliminated and arectifier bridge circuit is used to initiate self-oscillation in thesecond transistor circuit.

In order to properly allow for the load current taken from theelectrical generator, a resistor having a negative temperaturecoefiicient is used to change the operating range of the control meanswhen necessary.

In order to prevent the output current of the generator to increase thevalues potentially dangerous for the generator, an embodiment of theinvention includes conductor means in circuit with the input and outputcircuits of the second transistor and adapted to be in substantiallyblocked condition as long as the voltage drop across a resistor in theoutput circuit is below a preselected value, but to become conductivewhen this voltage drop exceeds the preselected value. The voltage dropis transmitted by the conductor means to the output circuit of thesecond transistor so that the voltage output of the generator remainssubstantially constant as long as the output current does not exceed apredetermined amount corresponding to said preselected voltage dropvalue, but decreases rapidly as soon as the predetermined current amountis exceeded.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings, inwhich:

Fig. 1 is an electrical schematic diagram of a first embodiment-of thepresent invention;

Fig. 2 is a partial schematic diagram of a second embodiment of thepresent invention;

Fig. 3 is an electrical diagram of a third embodiment of the presentinvention; and

Fig. 4 is an electrical diagram of a modification of the embodimentillustrated by Fig. 3.

Referring to the drawings and more particularly to Fig. 1, it can beseen that the generator G is provided with brushes a and b. The a brushis the negative brush and is directly connected to the electrical groundwhile the b brush is the positive brush and is connected by means ofconductors 51 and 52 to the emitter electrode E1 of a transistor 10. V aV p r The transistor has a collector electrode C1 connected by means ofa conductor 53 to one side of the field winding F of the generator G.The other end of the shunt field exciting winding F is connected bymeans of a conductor 54 directly to ground.

It is apparent that the generator G has a rotatable armature which iscoupled to the motor of the motor vehicle and which generates a voltagewhich is produced between the brushes a and b in the indicated polarity.The voltage generated by the generator G is indicated by the arrow U.

The transistor 10 also has an input circuit including the base electrodeB1 which is connected to ground through the resistor 11. Connected inparallel with the resistor 11 is a capacitor 35. I

From the portion of the figure so far described, it is apparent that thegenerator G has a self-excited shunt field winding F, the excitingcurrent being produced in the Winding F by the voltage produced acrossthe brushes a and b. The magnitude of the current Je which is theexciting current flowing through the field winding F depends upon thepotential distribution between the electrodes of the transistor 10.

That is, the exciting current for the field winding F is the outputcurrent obtained on the conductor 53 from the collector electrode C1 ofthe transistor 10. The magnitude of this current depends upon thepotential difference between the emitter E1 and the base electrode B1.It is apparent that the emitter electrode will be maintained at the samepotential as the voltage output appearing at the brush b. Output currentwill be obtained at the collector electrode C1 as long as the potentialof the base electrode B1 is equal to or smaller than the potential atthe emitter electrode E1. As the potential of the base electrode israised, the magnitude of the output current appearing at the conductor53 will decrease. Similarly as the potential applied to the baseelectrode B1 decreases, the magnitude of the output current appearing onthe conductor 53 will increase.

It is also clear that the magnitude of the current flowing through theshunt field winding P will determine the voltage output of the generatorG for the particular speed at which the generator is being rotated bythe motor of the motor vehicle.

To further complete the circuit of Fig. 1, it can be seen that thepositive brush b is also connected to the positive terminal of anauxiliary battery H, the negative terminal of which is connected to theemitter electrode E2 of a second transistor 20. The output circuit ofthe transistor 20 includes the conductor 56 connected to the collectorelectrode C2 thereof and also connected at the other end to the junctionpoint between windings 22 and 23. Windings 22 and 23 are two windings ofa transformer T having an iron core 21. The transformer T also has athird winding 24 wound about the iron core 21. That is, the transformerT includes three windings 22, 23, and 24, each wound about the iron core21 in the same winding direction.

It can be seen that the junction point between the windings 23 and 24 isconnected to the electrical ground of the apparatus While the distantend of the winding 22 is connected to the base electrode B1 of thetransistor 10 by means of the half-Wave rectifier 29. Similarly, theother end of the winding 24 is connected to the base electrode B1 bymeans of the half-wave rectifier 28.

This end of the winding 24 is also connected to the base electrode B2 ofthe transistor 20 by means of the series combination of the resistors 27and 26. The base electrode B2 of the transistor 20 is also connected tothe positive voltage supply conductor 51 by means of an adjustableresistor 25. The resistors 25, 26 and 27 form a voltage divider circuitbetween the positive conductor 51 and the electrical ground. The winding24 has a very low resistance and accordingly does not form a substantialpart of the voltage divider arrangement.

The resistor 27 is a resistor having a negative temperature coeflicientso that the resistance thereof decreases as the temperature of theresistor 27 increases. To vary the temperature of the resistor 27 in apredetermined manner to be described subsequently, a heating coil 30 iswound about the resistor 27 and is connected at one of its ends by meansof a conductor 31 to the positive supply conductor 51. The other end ofthe coil 30 is connected by means of a half-wave rectifier 34 to thepositive terminal of a battery 32. It is apparent that the battery 32may be the conventional storage battery utilized in the motor vehicles.Also shown in schematic form is a load 33 which is adapted to beconnected across the battery 32 by means of a switch 57. It is clearthat when the switch 57 is closed, and voltage is generated by thegenerator G, current flows through the conductors 51, 31, the coil 30and the rectifier 34 to the load 33. This current is also used forcharging the battery 32 when the potential of the generator issufficiently large to carry out this function.

The regulating function of the circuit of Fig. 1 is carried out in thefollowing manner: It is seen that the emitter electrode E2 of thetransistor 20 is arranged to be at a lower voltage than the positivevoltage appearing at the conductor 51. This lower voltage is a fixedamount lower than the positive conductor 51 due to the fixed biasingvoltage introduced by the battery H. When the motor vehicle startsmoving and the generator starts turning and generating voltage, thevoltage appearing on the conductor 51 is divided by the voltage dividercircuit including the resistors 25, 26 and 27. Therefore, the baseelectrode B2 of the transistor 20 has a potential applied theretodepending upon the voltage drop in the adjustable resistor 25. Thevalues of the various components of the circuit'are arranged so thatthis voltage drop in the resistor 25 will be smaller than the biasingnegative voltage introduced by the battery H. Accordingly, initially,the potential of the base electrode B2 will be higher than the potentialof the emitter electrode E2. The transistor 20 will then be in blockedcondition and no output current J will appear on the output conductor 56thereof.

Under these conditions, the exciting current Ie flowing through thefield winding F will depend only upon the potential distribution betweenthe various electrodes of the transistor 10 connected in circuit withthe winding F. As the voltage increases on the conductor 51, the voltagedrop across the resistor 25 will increase until it is substantiallyequal to the amount of biasing potential applied to the emitterelectrode E2. At this point, the transistor 20 will change from blockedcondition to conductive condition. Therefore, some output current willappear on the output conductor 56 and some base electrode current willflow through the lower portion of the voltage divider.

The output current J appearing on the conductor 56 will flow through thewinding 23 to the electrical ground returning to the negative brush ofthe generator. This will induce a fiux change in the iron core 21 aboutwhich the winding 23 iswound. 'This flux change in the core 21 willproduce a voltage across the coil 24 in a direction as indicated by thearrow U2.

The polarity of the voltage U2 is in such a direction as to decreasefurther the potential of the base electrode B2 of the transistor 20.Therefore, the feedback effect will cause a greater output current toappear on the output conductor 56. This large increase in the outputcurrent 1 appearing on the conductor 56 ll not p od ce a Correspondingchange in the winding 24 since the iron core 21 soon becomes saturatedand the increased current flowing through the winding 23 has nosubstantial effect on the flux in the core 21. Finally, the outputcurrent I reaches a maximum value which is predicated on the maximumvalue of the base current and the other elements of the transistor. Whenthis maximum value is reached, the voltage U2 produced in the winding 24disappears and the potential of the base electrode B2 quickly rises to ahigher value. Accordingly the base current of the transistor 20 can nolonger be sustained at its high level. The magnitude of the base currentaccordingly decreases carrying with it a corresponding decrease in theoutput current I quickly cutting off such output current.

The winding 23 acts to oppose this rapid change in the magnitude of theoutput current I and in so doing changes the flux distribution throughthe core 21 in the opposite direction so that a voltage U2 shown by thedotted arrow in Fig. 1 is induced in the coil 24. It is apparent thatthe second induced voltage U2 is in the opposite direction from theinitial induced voltage. This second induced voltage U2 acts to quicklyraise the base electrode above the potential of the emitter electrode E2of the transistor 20. The transistor 20 therefore changes back to theblocked condition thereof.

At this point the cycle is complete and the transistor 20 can start anew cycle as soon as the preselected level of the voltage appearing onthe conductor 51 is again reached. It is apparent that this preselectedlevel is the level wherein the voltage drop across the resistor 25 willequal the negative biasing potential introduced by the battery H.

Since the voltages U2 and U2 induced in the winding 24 in accordancewith the changes of the collector current J are applied to the potentialof the base electrode B2 which is in the input circuit of the transistor20, an amplification elfect is achieved which corresponds to aself-excited electrical oscillation. In this self-oscillation, thetransistor 20 operates between a conductive condition having a highcollector current J and a blocked condition having a low collectorcurrent J This is substantially the equivalent of a mouostable blockingoscillator which oscillates at a repetition rate determined by thedesired preselected level of the generator voltage and the setting ofthe resistor 25.

The voltage impulses U2 and U2 are applied by means of the rectifiers 28and 29 to the capacitor 35. The value of the capacitor 35 is chosen tohave a time constant which corresponds to the particular type ofgenerator being used. Each time the potential impulse is applied acrossthe capacitor 35, the potential of the base electrode B1 of thetransistor is raised. This operates to decrease the collector currentappearing on the output conductor 53, which collector current is theexciting current Ie for the shunt field winding F. Therefore, thevoltage output of the generator is automatically decreased each timethat an impulse is applied to the capacitor 35. The decrease of theoutput voltage of the generator G has the effect of blocking thetransistor 20 which will remain blocked until the generator G is able toagain reach the preselected level.

In order to avoid overloading the generator G by means of too high aload consumption, the load current obtained from the generator G flowsthrough the conductors 51 and 31 to the coil 3% wound about the resistor27. The larger the load current produced by the geneator and consumed bythe load 33, the greater will be the amount of heat produced in the coil30.

As the heat produced by the coil 30 increases, the resistance of thenegative temperature coeilicient 27 will decrease. it is apparent thatthis resistor 27 will then play a smaller part in the voltage dividercircuit and have less of a voltage drop thereacross. Therefore, theresistor 25 will have a greater voltage drop in proportion and the baseelectrode B2 of the transistor 20 6 will reach the potential of theemitter E2 at a lower level of the generated voltage.

It can therefore be seen that the effect of the coil 30 which is aheating coil, is to displace the voltage zone of operation in which theregulating apparatus operates.

The rectifier 34 arranged between the coil 30 and the battery 32 isprovided in order to prevent a discharge from the battery 32 to thegenerator G when the respective potentials might so dictate. In oneembodiment of the apparatus constructed in the manner of Fig. l, thefollowing values for the elements are used. The resistor 11 had aresistance of 100 ohms; the center winding 23 of the transformer T hadapproximately windings and an inductance of 20 millihenries; the voltageintroduced by the negative biasing battery H was in the order of 2volts; the adjustable resistor 25 had a resistance of approximately 10ohms while the resistor 26 had a resistance of between 40 and 50 ohms;the negative temperature coefiicient resistor 27 had a resistance of 10ohms in its cold state while the resistance of the winding 24 wassubstantially negligible; and the capacitor 35 had a capacitance of 50microfarads.

Additional elements can be added to the circuit of Fig. 1 as shown indotted lines. For example in order to avoid undesired voltage peaksbeing introduced in the field winding F when the transistor 10 may be inblocked condition, a rectifier 36 can be arranged in parallel with thewinding F. This rectifier will have practically no current flowingtherethrough during the constant excitation of the field winding. If acrystal diode is used as the rectifier 36 a limiting resistor 37 can bearranged in series therewith. With generators of very heavy loadcapacity it might be advantageous to arrange a damping resistor 38 inparallel with the field winding F,

Referring now to Fig. 2, a modification of the arrangement shown in Fig.1 will be described wherein no separate auxiliary battery H is needed.In Fig. 2, only that portion of the circuit which is different from theportion of Fig. 1 is indicated. Otherwise the circuit remains the same.

In this circuit arrangement of Fig. 2, it can be seen that the positivesupply conductor 51 is connected to the emitter electrode E of thetransistor 40 by means of two series-connected rectifiers 41 and 42. Thetransistor 40 takes the place of transistor 20 of the arrangement inFig. 1. Arranged between the power supply conductor 51' and the groundconductor is a voltage divider consisting of a variable resistor 44, aresistor 45 and the low resistance winding 24. As before, the baseelectrode B of the transistor 40 is connected to the junction point ofthe resistor 44 and the resistor 45. The emitter electrode E of thetransistor 40 is connected to ground by a resistor 43.

The remainder of the circuit of Fig. 2 includes the rectifier 49, thebattery 32 and the load 33'.

It can be seen that the circuit of Fig. 2 provides a bridge circuitwherein the voltage applied from the generator G is applied across adiagonal of the bridge to the terminals 61 and 62 thereof. The remainingtwo terminals of the bridge include the terminals 63' and 64. It can beseen that the transistor 40 is connected in this diagonal of the bridge.

Accordingly, in operation, the potential of the base electrode B willdecrease to the potential of the emitter electrode B when the voltage ofthe generator G increases to the preselected level and provides asubstantially large increase in the adjustable resistor 44. This voltagedrop across the resistor 44 must equal the voltage drop across therectifiers 41 and These rectifiers have sharply curving characteristicsand accordingly the equalizing preselected level is reached inaccordance with the adjustment of the resistor 44. When this occurs, thetransistor 40 changes from its blocked condition to its conductivecondition. Therefore an output current is provided on the outputconductor 66 thereof taken from the collector electrode C. Thisconductor 66 corresponds to the conductor 56 of Fig. 1 and accordinglyis connected between the coils of the transformer T in the same manner,namely between coils 22 and 23. Therefore the circuit of Fig. 2functions in the same manner as the circuit of Fig. 1 but requires noauxiliary battery.

In order to produce the equalized voltage between the base electrode Band the emitter electrode E of the transistor 40, a crystal diode 46 canbe used which has a substantially rectilinear characteristic in theblocking zone thereof. One such crystal diode is called a Zener diodeand is shown in dotted lines in Fig. 2. This crystal diode 46 can beused in place of the rectifiers 41 and 42. The advantage of utilizingthe diode instead of the rectifiers 41 and 42 is that a resistor 47 canbe arranged in series therewith to have a much higher resistance thanthe resistor 43.

In order to produce a lower preselected level at which to regulate thevoltage of the generator with increasing load in the arrangement of Fig.2, it is advantageous to arrange a resistor 48 as shown in the powersupply conductor 51 in dotted form in Fig. 2. This resistor can have aresistance in the order of milliohms, for example. The junction pointbetween the resistor 48 and the resistor 44 is utilized for the outputcurrent going via a semiconductor diode 49 to the load 33' and thebattery 32. As the magnitude of the output current of the generator Gflowing through the conductor 51' increases, the voltage drop across theresistor 48 will also increase. In this manner, the transistor 40 willbe changed from its blocked condition into its conductive condition at alower value of the generator voltage. Therefore the regulating efiect ofthe self-excited transistor 40 following a linear characteristic will beintroduced to maintain the voltage output of the generator G at suchlower preselected level.

In the operation of the embodiments shown in Figs. 1 and 2, it is clearthat the second transistor, either transistor 20 or transistor 40,operates to control the potential distribution of the electrodes of thetransistor which is connected in circuit with the field winding F of thegenerator. As the controlling transistor oscillates between blocked andconductive conditions, the exciting current flowing through the windingF is changed in a direction to regulate the voltage output of thegenerator G at its preselected level.

In Fig. 2 it is clear that the rectifiers 41 and 42 or the crystal diode46 are arranged to provide the desired non-linear resistancecharacteristics to achieve the proper potential distribution of theelectrodes of the transistor 40 to change the transistor from is blockedcondition to its conductive condition.

Referring now to Figs. 3 and 4, modified embodiments of the inventionare based on the idea to provide in the input or control circuit of themeans producing a selfexcited oscillation a resistor connected in thecurrent output circuit of the generator and to apply the voltage dropappearing across that resistor to said means by way of conductor meansadapted to be in substantially blocked condition as long as the voltagedrop is below a preselected value, while said conductor means areconductive when the voltage drop exceeds that preselected value.

Suitable conductor means for this purpose are active or passive diodemeans to which a negative bias voltage is applied, or which have alinear V-I characteristic which has however a distinct break at a pointcorresponding to a critical voltage-current ratio. A particularly simplearrangement is obtained by using as a conductor means a crystal diodeadapted to produce the so-called Zener effect. Figs. 3 and 4 illustratetwo embodiments incorporating the above-mentioned features. Figs. 3 and4 are generally quite similar to the above-described Figs. 1 and 2 sothat hereinafter only those portions of these diagrams will be describedin detail which differ from those shown by Figs. 1 and 2. Referencenumerals and letters of parts that are substantially identical and havethe same function as those illustrated in Figs. 1 and 2 are the same asin Figs. 1 and 2.

Referring specifically to Fig. 3 it can be seen that the transformerThas a (fourth winding 27:: which is connected in series with conductormeans 59, 51a as will be described below. Connected in the main line 51"leading from the generator G, positive terminal 1;, to the battery 32 orload 33, is a resistor R in such a manner that the potential at theemitter E is lower than existing at the terminal b when the generatorvoltage U is higher than that of the storage battery 32 so that anoutput or charging current 1;, flows from the positive terminal 12 tothe positive pole of the battery through said resistor R. From a point Sbeyond the resistor R, i.e. on the side remote from the generator, abranch line leads to a silicon rectifier 42 which, together with aseries connected resistor 43 constitutes a voltage divider to which isconnected the emitter E of the transistor 2%. On the input side of thetransistor 20 the base electrode B is connected on one side via avariable resistor 25 to the resistor R, and on the other hand also tothe minus terminal a of the generator via a resistor 26 and theseries-connected winding 24.

By way of example it may be stated that in a preferred embodiment asillustrated the resistor 11 is of the magnitude of 100 ohms, the winding23 has approximately turns and 20 mh., the resistor R is of themagnitude of 40 milli-ohms, the variable resistor 25 is of the magnitudeof approximately 10 ohms, the resistor 26 is of the magnitude ofapproximately 40 to 50 ohms and the winding 24 has comparatively lowresistance.

The resistors 25, 26 and the ohmic resistance of the winding 24constitute one branch, and the rectifier 42 of the resistor 43constitutes the other branch of a bridge circuit which has a non-linearcharacteristic. The voltage appearing in the diagonal of the bridge isbound to change more than in proportion to changes of the generatorvoltage U from its preselected or nominal value, because of thepronounced curvature of the characteristic of the rectifier 42.

The operation of the whole arrangement is easily understood if onestarts from considering that the voltage U appearing at the terminals aand b of the generator G is increasing and that the resistor 25 is soadjusted that at the moment when the voltage U reaches a preselectedvalue, the voltage drop across the resistor 25 causes the base B to havethe same potential as the negatively biased emitter E of the transistor2e. On account of this the transistor 20 becomes conductive and causes acollector current 1 to flow which induces in the winding 24 a potentialindicated by the arrow U This potential U is so directed that the base Bof the transistor 20 is made even more negative with respect to theemitter E with the result that a rapidly increasing base current (themaximum value of which is determined by the magnitude of the inducedvoltage U and by the magnitude of the resistors 26 and 27) andconsequently also a rapidly increasing a collector current I isproduced. The voltage U induced by the collector current I during itsincrease changes but little. The collector current, however, reachesvery soon its maximum which is determined by the maximum value of thebase current J and by the structural characteristics of the transistor.As soon as this maximum value is reached, the voltage U induced in thewinding 24 practically disappears and the potential of the base Breturns abruptly to a higher level so that the base current I cannot bemaintained on its preceding level. Consequently, also the collectorcurrent J is reduced. The inductivity of the winding 23 opposes such achange of the collector current and therefore generates a voltageimpulse. which is symbolized in Fig. 3 by the broken line arrow U' Thetransistor 20 is rendered completely nonconductive by this voltage im- 9pulse and remains in this condition until the voltage impulse U' iscompletely terminated. Then, the whole cycle described above can startagain as soon as the output voltage U of the generator G reaches againthe preselected value.

Since the voltages U and U' induced in the winding 24 on account of thechanges of the collector current J influence the potential of the base Band consequently the input circuit of the transistor 26 in such a mannerthat said changes of J are intensified, a self-excited electricaloscillation is generated while the transistor 29 alternates between astate of high and a state of low collector current I in a manner similarto that of a monostable blocking oscillator, whenever the increasinggenerator voltage U has risen up to the preselected value determined bythe setting of the variable resistor 25.

The voltage impulses U and U are transmitted through the rectifiers 28and 2? to a charging condenser 35 the size of which is chosen inconformity with the time constant of the generator. The size of the.condenser is prferably approximately 25 to 50 2F and the condenser isconnected in parallel with the base resistor 11 to the base B of thefirst transistor 10. Each one of the voltage impulses has the effectthat the potential of the base B is briefly raised and the transistorsubstantially reduces the exciter current I whereby the output voltageof the generator is reduced. If the generator voltage U decreases belowthe preselected value, the transistor 20 remains in blocked conditionand no impulses tending to lower the output voltage are transmitted tothe transistor 10, until the generator has excited itself so as to reachagain the predetermined value of its output voltage. This procedurerepeats in rapid sequence as described, as long as the output current Jis either equal to zero or has a constant value.

The special feature of the embodiments illustrated by Figs. 3 and 4consists in the fact that for preventing the generator to be overloaded,the output current is caused to flow through the resistor R. Ahead ofthe resistor R the above-mentioned branch line including line a diode 50and in series therewith a transformer winding 27 is connected to themain line 51, the diode 50 being of a type which possesses a distinctbreak in its linear characteristic at a point corresponding to a certainvoltagecurrent ratio. In the preferred embodiment according to Fig. 3 adiode consisting of a crystal diode 51a adapted to produce the so-calledZener effect has been found particularly useful an eifective.

In the embodiment according to Fig. 3 the Zener diode 51a together withthe series-connected transformer winding 27a is connected in parallelwith the terminals :1 and b of the generator G, and obtains thereforepractically the full voltage U. As long as no output or charging currentI flows, no voltage drop appears across the resistor R. As the current,however, increases the voltage drop across the resistor R increases andthe transistor 20 is so controlled by the non-linear bridge circuit 42,43; 25, 27, 24 that the generator voltage U rises by an amount equal tothe voltage drop across R. In this manner, the potential at the point Sis kept practically constant. The magnitude of the resistor R is sochosen that the portion of the generator voltage U applied to the Zenerdiode 51a reaches its critical amount when the current 1;, exceeds themaximum value permissible as a load for the generator. In that moment,the Zener diode 51a that had been in blocked condition up to then, isrendered conductive so that a current flows through the transformerwinding 27a whereby in the other windings of the transformer T voltageimpulses are generated by induction, these impulses having the samepolarity as the voltage U shown by an arrow for the winding 24. Onaccount of these additional voltage increments the potential of the baseB of the transistor 20 is reduced and the transistor 20 transmits to thetransistor 10 through the winding 23 a blocking impulse with the eifectthat the generator voltage decreases. At the same time the partialvoltage applied to the Zener diode 51a decreases below the criticalvalue of this diode so that also the output current is reduced.

The modified embodiment according to Fig. 4 advantageously differs fromthe embodiment according to Fig. 3 because the limitation of the maximumcurrent 1;, is independent to the value of the generator voltage output.

According to Fig. 4 the shunt field winding F of the generator G is alsoconnected to the collector C of a transistor 10 whose emitter E isconnected to the posi tive terminal b of the generator while its base Bis connected through a resistor 11 with the minus terminal a of thegenerator 4. The base B is likewise influenced by a control transformerT comprising three series-connected windings 22, 23 and 24 throughrectifiers 28 and 29. The transformer is supplied by the transistor 20whose emitter-base circuit constitutes the one diagonal of a bridgecircuit having non-linear characteristic. The bridge circuit isconstituted on one hand by the variable resistor 25 and the fixedresistor 26 and the negligibly small ohmic resistance of the winding 24,on the other hand by the fixed resistor 43 and the silicon rectifier 42which serves as a bridge component having a non-linear characteristic.

In contrast with the arrangement according to Fig. 3, the embodimentaccording to Fig. 4 is characterized by the fact that the voltage dropappearing across the resistor R depending upon the current I isintroduced into the non-linear bridge circuit which serves to controlthe preselected value voltage output. A non-linear voltage dividerconsisting of a crystal diode 51a and a fixed resistor 52a ofapproximately .5 ohm is connected in parallel with the load resistor R.At a point between the just-mentioned components of the voltage dividera variable resistor 25 is connected in circuit. As long as the voltagedrop across the resistor R is small, the crystal diode has acomparatively great resistance; how ever, when the voltage drop is largethe resistance of the crystal diode is comparatively small.

On account of this characteristic of the diode 51a as a function of theapplied voltage the output voltage U of the generator is keptapproximately constant as long as the current I rises only up to apredetermined value, however the voltage U decreases rapidly when thecurrent exceeds the predetermined value.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofregulating apparatus differing from the type described above.

While the invention has been illustrated and described as embodied inapparatus for regulating the voltage output of shunt wound generators,either self-excited or separately excited, it is not intended to belimited to the details shown, since various modifications and structuralchanges may be made without departing in any way from the spirit of thepresent invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended Within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. In an apparatus for regulating the voltage output of an electricalgenerator having a shunt field exciting winding adapted to have excitingcurrent flow therethrough, in combination, a first and a secondtransistor circuit and transformer means operatively connecting saidtransistor circuits, said first transistor circuit including a firsttransistor connected in circuit with the shunt winding of the electricalgenerator for adjusting the exciting current flowing through the shuntwinding in accordance with the impedance of said first transistor; andsaid second transistor circuit including a second transistor having aninput circuit connected in circuit with the output of the generator andhaving an output circuit connected in circuit with said first transistorfor producing an output current which varies the impedance of said firsttransistor, at least a portion of said output circuit of said secondtransistor being connected to said input circuit thereof so that atleast a portion of said output current is fed back to the input thereofto produce self-oscillation in said second transistor for varying theimpedance of said first transistor in a selected manner in accordancewith the magnitude of the voltage output of said electrical generator.

2. In an apparatus for regulating the voltage output of an electricalgenerator having a shunt field exciting winding adapted to have excitingcurrent flow therethrough, in combination, a first and a secondtransistor circuit and transformer means operatively connecting saidtransistor circuits, said first transistor circuit incuding a firsttransistor having a plurality of electrodes connected in circuit withthe shunt winding of the electrical generator for adjusting the excitingcurrent flowing through the shunt winding in accordance with thedifference of potentials between said electrodes of said transistor andthereby adjusting the voltage output of the generator; means forproducing an initial difference of potential distribution between saidelectrodes to thereby produce a predetermined amount of exciting currentin the shunt field winding; and said second transistor circuit includinga second transistor having an output circuit connected in circuit withthe output of the generator and having an output circuit connected incircuit with said first transistor for producing an output current whichvaries said potential distribution between said electrodes of said firsttransistor, at least a portion of said output circuit of said secondtransistor being connected to said input circuit thereof so that atleast a portion of said output current is fed back to the input thereofto produce self-oscillation in said second transistor after the voltageoutput of the generator reaches a preselected level, whereby any changein the volt-age output of the electrical generator after saidpreselected level is reached changes the output current of said secondtransistor to produce a corresponding change in said potentialdistribution of the electrodes of said first transistor and in theexciting current flowing through the shunt field winding, therebychanging the voltage output of the generator to maintain the same atsaid preselected level.

3. In an apparatus for regulating the voltage output of an electricalgenerator having a shunt field exciting winding adapted to have excitingcurrent flow therethrough, in combination, a first transistor connectedin circuit with the shunt winding of the electrical generator foradjusting the exciting current flowing through the shunt winding inaccordance with the impedance of said first transistor; a secondtransistor having an input circuit connected in circuit with the outputof the generator and having an output circuit connected in circuit withsaid first transistor for producing an output current which varies theimpedance of said first transistor; and a transformer connected incircuit with said output circuit of said second transistor and having awinding connected in circuit with said input circuit of said secondtransistor sothat at least a portion of said output current is fed backto the input thereof to produce self-oscillation in said secondtransistor for varying the impedance of said first transistor in apreselected manner in accordance with the magnitude of the voltageoutput of said electrical generator.

4. Apparatus as claimed in claim 3 wherein said transformer has threewindings connected in series, one of said windings being connected incircuit with said output circuit of said second transistor, the secondof said windings being connected in circuit with the input circuit ofsaid second transistor and the third of said windings is connected incircuit with said first transistor.

5. Apparatus as claimed in claim 15, wherein said bridge circuitarrangement includes at least one non-linear resistor.

6. Apparatus as claimed in claim 5 wherein said nonlinear resistor is arectifier.

7. Apparatus as claimed in claim 5 wherein said nonlinear resistor is aZener diode.

8. In an apparatus for regulating the voltage output of an electricalgenerator having a shunt field exciting winding adapted to have excitingcurrent flow therethrough, in combination, a first transistor having aplurality of electrodes connected in circuit with the shunt winding ofthe electrical generator for adjusting the exciting current flowingthrough the shunt winding in accordance with the difference ofpotentials between said electrodes of said transistor and therebyadjusting the voltage output of the generator; means for producing aninitial difference of potential distribution between said electrodes tothereby produce a predetermined amount of exciting current in the shuntfield winding; a second transistor having an input circuit connected incircuit with the output of the generator and having an output circuitconnected in circuit with said first transistor for producing an outputcurrent which varies said potential distribution between said electrodesof said first transistor; and a transformer connected in circuit withsaid output circuit of said second transistor and having at least onewinding connected in circuit with said input circuit of said secondtransistor so that at least a portion of said output current of saidsecond transistor is fed back to the input thereof to produceself-oscillation in said second transistor after the voltage output ofthe generator reaches a preselected level, whereby any change in thevoltage output of the electrical generator after said preselected levelis reached changes the output current of said second transistor toproduce a corresponding change in said potential distribution of theelectrodes of said first transistor and in the exciting current flowingthrough the shunt filed winding, thereby changing the voltage output ofthe generator to maintain the same at said preselected level.

9. In an apparatus for regulating the voltage output of an electricalgenerator having a shunt field exciting winding adapted to have excitingcurrent flow therethrough, in combination, a first and a secondtransistor circuit and transformer means operatively connecting saidtransistor circuits, said first transistor circuit including a firsttransistor connected in circuit with the shunt winding of the electricalgenerator for adjusting the exciting current flowing through the shuntwinding in accordance with the impedance of said first transistor; andsaid second transistor circuit including a second transistor having aninput circuit connected in circuit with the output of the generator andhaving an output circuit connected in circuit with said first transistorfor producing an output current which varies the impedance of said firsttransistor, a resistor connected in said input circuit of said secondtransistor for producing a voltage drop across said resistor dependingupon the output current of said generator, and conductor means connectedin circuit with said input circuit of said second transistor fortransmitting said voltage drop to said input circuit, said conductormeans being in substantially blocked condition as long as said voltagedrop is below a preselected value, but becoming conductive when saidvoltage drop exceeds said value, at least a portion of said outputcircuit circuit of said second transistor being connected to said inputcircuit thereof so that at least a portion of said output current is fedback to the input thereof to produce self-oscillation in said secondtransistor for varying the impedance of said first transistor in apreselected manner in accordance with the magnitude of the voltageoutput of said electrical generator, said voltage output remainingsubstantially constant as long as said output current remains below apredetermined valve corresponding to said preselected voltage dropvalue, said voltage output decreasing rapidly when said output currentexceeds said predetermined value.

10. An apparatus as set forth in claim 9, wherein said conductor meansis a diode device having a V-I characteristic which possesses a distinctbreak at a critical voltage-current ratio.

11. An apparatus as set forth in claim 9, wherein said conductor meansis a diode device and includes means for applying a negative biaspotential thereto.

12. An apparatus as set forth in claim 10, wherein said diode device isa crystal diode adapted to produce the Zener effect.

13. An apparatus according to claim 9, including transformer meanshaving at least one coil connected in series with said conductor meansand being connected in circuit with said first transistor for applyingto the latter impulses capable of blocking it.

14. An apparatus according to claim 9, wherein said resistor isconnected in the output circuit of said generator and said conductormeans is connected to said generator output circuit at a point beyondsaid resistor remote from said generator; said apparatus furtherincluding an auxiliary resistor in series connection between saidconductor means and one pole of said generator; and a bridge circuit ofnon-linear characteristic comprising two voltage-divider circuitsrespectively connected with one end jointly to the other pole of saidgenerator, while the other ends of said voltage dividers arerespectively connected to the opposite ends of said auxiliary resistor,said input circuit of said second transistor being connected as onediagonal of said bridge circuit.

15. An apparatus as claimed in claim 3, including a bridge circuitarrangement, said second transistor being connetced in the diagonal ofsaid bridge circuit, said bridge circuit having two input terimnalsconnected in circuit with the output of said generator.

16. An apparatus as claimed in claim 3, including impedance meansconnected in circuit with said second transistor and with the voltageoutput of said generator for controlling the rate at which the impedanceof said first transistor is varied.

17. An apparatus as claimed in claim 3, wherein impedance means areconnected in circuit with said second transistor and said voltage outputof said generator for changing the level of said voltage output inaccordance with the magnitude of the current ouput of said generator.

18. An apparatus as claimed in claim 16, wherein said impedance meanshave a negative temperature coefficient.

19. An apparatus as claimed in claim 17, wherein said impedance meanshave negative temperature coefiicient.

20. An apparatus as claimed in claim 3, including means for applying tosaid second transistor a bias potential between its emitter and baseelectrodes of such a magnitude that said second transistor becomesconductive only when the voltage output of said generator surmounts apredetermined value, the frequency of said selfoscillation dependingmainly on the inductivities of said transformer.

21. An apparatus as claimed in claim 3, including a non-linear bridgecircuit comprisnig as one bridge arm, in circuit, an auxiliary source ofdirect current potential, the emitter-collector circuit of said secondtransistor and a winding of said transformer, and as a second bridgearm, in circuit, resistive voltage divider means and another winding ofsaid transformer, the base electrode of said second transistor beingconnected to a junction point within said voltage divider means, and theoutput of said generator being connected as a diagonal of said bridgecircuit to the respective junction points of said bridge arms.

22. An apparatus as claimed in claim 3, including a non-linear bridgecircuit comprising as one bridge arm, in circuit, rectifier means havinga curved current voltage characteristic, the emitter-collector circuitof said second transistor and a winding of said transformer, and as asecond bridge arm, in circuit, resistive voltage divider means andanother winding of said transformer, the base electrode of said secondtransistor being connected to a junction point within said voltagedivider means, and the output of said generator being connected as adiagonal of said bridge circuit to the respective junction points ofsaid bridge arms.

23. An apparatus as claimed in claim 9, wherein said resistor isconnected in the output circuit of said generator, and said conductormeans is connected to a junction point in said generator output circuitbetween said generator and said resistor, said apparatus furtherincluding transformer means having one coil connected in series withsaid conductor means, and having at least one other coil connected withthe input circuit of said second transistor for causing the latter toproduce selfoscillation when said voltage drop exceeds a predeterminedvalue.

References Cited in the file of this patent UNITED STATES PATENTS2,740,086 Evans et al Mar. 27, 1956 2,809,301 Short Oct. 8, 19572,866,944 Zelina Dec. 30, 1958 2,886,763 Zelina May 12, 1959

